An Organic Light-Emitting Device (OLED) is a light-emitting device taking an organic solid-state semiconductor as a light emitting material, and it has a broad prospect for application due to advantages such as simple fabrication process, low cost, low power consumption, high brightness, and wide range of operating temperature.
The OLED typically comprises an anode layer, a cathode layer and a light-emitting layer disposed between the anode layer and the cathode layer. A light-emitting mechanism of the OLED is as follows: when a voltage is applied between the anode layer and the cathode layer, holes injected from the anode layer side overcome an interface potential barrier and are transmitted to the light-emitting layer, electrons injected from the cathode layer side overcome an interface potential barrier and are transmitted to the light-emitting layer, the holes and the electrons arriving at the light-emitting layer recombine in the light-emitting layer to form excitons, and the excitons jumps to a lower energy state to emit light, which is called electroluminescence. In this process, if an excited-state electron spin pairs up with a ground-state electron, the exciton is a singlet and light emitted thereby is so-called fluorescence; if the excited-state electron spin and the ground-state electron are unpaired and parallel, the exciton is a triplet and light emitted thereby is so-called phosphorescence.